Doing a Vader spinoff would probably do more damage than anything else. It's one of those characters you want to use the least because it would diminish his presence as a character on the Original Trilogy every second he's on screen in anything else.

This, and its applicable for the whole franchise... I'm a Star Wars FREAK, But it still needs to be a massive event when we get a Star Wars film, I don't want us to get so many that its waters down Star Wars on the big screen, like the EU and TCW tends to do to themselves. Quality not Quantity.